POS0413 SEX DIFFERENCES IN A MURINE MODEL OF OSTEOARTHRITIS
Authors: S. Bharde, S. Caxaria, P. Celik, S. Sikandar
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Pain is the leading cause of disability in osteoarthritis (OA), but the correlations between structural changes of the joint and functional changes in pain-related outcomes remains poorly understood. Animal models of OA have poor translational outputs to improve pain management in OA<sup>[1,2]</sup>. Moreover, several studies demonstrate a higher prevalence of chronic pain in the female OA population<sup>[3,4]</sup> and sex differences that can give rise to distinct pain mechanisms in male and female rodents with OA<sup>[5]</sup>. <h3>Objectives</h3> We aim to define the translational value of a murine model of surgically-induced OA with meniscal/ligamentous injury (MLI), in terms of the progressive nature of joint degeneration, temporal delay in development of chronic pain following joint damage and potential sex differences. <h3>Methods</h3> <i>Model</i>: OA was induced in 10-week-old C57BL/6J mice under isoflurane anaesthesia with resection of the medial collateral ligament (MCL), meniscotibial ligament and removal of the medial meniscus. <i>Behaviour</i>: Sensory thresholds were assessed using the up-down von Frey, hindlimb capacitance, Hargreaves', hotplate and dry ice tests. Affective behaviours were measured using hotplate and open field assay. <i>In vivo electrophysiology</i>: Extracellular recordings of L4 dorsal horn neurones was performed in anesthetised mice. Mechanically and thermally evoked action potentials were quantified. <i>MicroCT</i>: Bone mineral density was measured along the growth plate and BoneJ was used for microarchitecture analysis to determine 3D geometric parameters. <i>Histological OA scoring and immunohistochemistry</i>: Coronal sequential paraffin sections were stained with Safranin-O for OA severity scoring using the Osteoarthritis Research Society International grading system. Additional knee sections were stained for neo-innervation using anti-PGP9.5. <i>RNASeq:</i> RNA was extracted from L3-L5 ipsilateral DRGs and differentially expressed transcripts generated by GeneWiz. <h3>Results</h3> We observed progressive development of persistent mechanical and cold hypersensitivity in MLI mice compared to Sham controls. We also observed contralateral hypersensitivity, indicative of nociplastic pain. Female mice expressed an earlier onset and greater extent of hypersensitivity compared to male mice. The temporal delay in the expression of hindlimb hypersensitivity correlates with a loss of cartilage integrity measured by OARSI scoring of the knee joint in both males and females. Affective behaviours are also correlated with changes in sensory thresholds, indicating emotional processing of nociceptive inputs form the injured knee. We observed greater PGP9.5 staining in female MLI mice and key transcriptional changes in DRG neurons. <h3>Conclusion</h3> Our data demonstrates that the MLI model reproduces clinical features of nociplastic pain and cartilage loss in OA. We identify structural changes in the knee joint that correlate with pain behaviour, as well as sex differences in knee innervation, transcriptomic profiles of primary sensory neurons and pain behaviour that is exacerbated in female mice, informing on sex specific pain mechanisms. This establishes the use of MLI surgery as a clinically relevant mouse model for OA pain. <h3>References</h3> [1]Cope, P.J., et al., <i>Models of osteoarthritis: the good, the bad and the promising.</i> Osteoarthritis Cartilage, 2019. 27(2): p. 230-239. [2]Hochberg, M.C., <i>Serious joint-related adverse events in randomized controlled trials of anti-nerve</i> [3]Mogil JS. Sex differences in pain and pain inhibition: Multiple explanations of a controversial phenomenon. Vol. 13, Nature Reviews Neuroscience. 2012. p. 859–66. [4]Srikanth VK, Fryer JL, Zhai G, Winzenberg TM, Hosmer D, Jones G. A meta-analysis of sex differences prevalence, incidence and severity of osteoarthritis. Osteoarthr Cartil [Internet]. 2005;13(9):769–81. [5]von Loga IS, Batchelor V, Driscoll C, Burleigh A, Chia SLL, Stott B, et al. Does Pain at an Earlier Stage of Chondropathy Protect Female Mice Against Structural Progression After Surgically Induced Osteoarthritis? Arthritis Rheumatol. 2020;72(12):2083–93. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.